In the operation of turbo engines there is the danger that the impingement of foreign bodies on the blades, or due to material fatigue, will sever fragments from the rapidly spinning rotor, thereby causing such fragments to fly off by centrifugal force. Considering the prevailing operating conditions of aero engines, weight considerations forbid thickening the walls in the endangered area sufficiently to safely keep a fragment from penetrating the wall of the engine casing. However, penetration must in any event be prevented, since in the case of aircraft, fragments penetrating the engine casing may produce severe damage, injur persons or damage important parts and so cause crashes.
For this reason, it has been the practice to fit rupture protection rings of lightweight, high tensile strength materials around the engine casing in the endangered areas to safely contain fragments. Suitable materials for such rupture protection rings notably are fiber-reinforced materials wrapped around the engine casing in the form of rovings or fibercloth. German Patent Publications DE-OS 2,950,752 and DE-OS 3,515,835 illustrate such rupture protection rings, where cloth layers of aramid fibers are wrapped in several layers which are interwoven. These constructions have the disadvantage that the highly elastic fibers are heavily expanded by an impact so that engine parts in close proximity to the engine casing may still be injured even if the fragment is contained. A great degree of expansion is nevertheless needed to produce stretch in the highly elastic fiber for maximizing its fragment containing or retaining action.
Another disadvantage afflicting conventional structures of this kind is seen in that the fibers--with their free ends at the edge of the rupture protection ring--are unable to transfer forces, whereby the volume available for energy absorption is reduced. Another disadvantage is seen in that a blade exiting near the ring edge will bend the edge up and slide over it. To prevent this, the rupture protection ring must be made much wider than is conventionally feasible--at a considerable weight penalty. French Patent Publication (FR-PS) 2,514,823 discloses a generic version with one or more rigid rings enveloping the engine casing, wherein the rings are attached to a shield-like section made of laminated fiber-cloth. This arrangement has the disadvantage that owing to the high shear load on the laminate, the energy absorption of the structure is rather low in relation to the fiber strength. The laminate is additionally disadvantaged by its high weight.